Hydraulic press with a pressure cell and a method and use for it, whose press body consists of prestressed lamellas

ABSTRACT

The present invention relates to a press of pressure cell type and a method for manufacturing a press body part. The press body part comprises a number of plate-shaped lamellar means having the planes of the plates oriented parallel to the planes of the plates of the adjacent lamellar means. Each lamellar means has a through hole which has the same centre axis as the hole of the adjacent lamellar means. Prestressing means which induce a compressing prestress acting in the planes of the plates are arranged on an external edge surface of the main part of the lamellar means. The invention also relates to a lamellar means of a press body part.

FIELD OF THE INVENTION

[0001] The present invention relates to a press of pressure cell type,which comprises a press chamber being enclosed by a force-absorbingpress body. The invention also relates to a method for manufacturing apress body part.

BACKGROUND ART

[0002] A press of pressure cell type generally comprises aforce-absorbing press body which defines a press chamber. In the upperpart of the press chamber, a press plate and a diaphragm of rubber oranother resilient material are arranged, which together form a pressurecell. The pressure cell communicates with a source of pressure andexpands when a pressure medium is supplied. In the lower part of thepress chamber, a structural support or a tray is arranged, whichcomprises a bottom plate having a tray frame. The tray supports aforming tool, a workpiece, a mat of rubber or another resilientmaterial, covering the forming tool and the workpiece.

[0003] Presses of pressure cell type are used, among other things, whenforming sheet-shaped blanks, for example sheets of steel or aluminium,to short series products within the aircraft industry and the motorindustry. The sheet is placed in the press in such a manner that one ofits sides faces a forming tool. The resilient diaphragm is arranged onthe other side of the sheet. A closed space between the diaphragm andthe press plate located above the diaphragm constitutes the pressurecell and this space is filled during the forming process with a pressuremedium. By pumping additional pressure medium into the pressure cell,the pressure is increased in the pressure cell and the resilientdiaphragm is pressed during stretching against the sheet which, in itsturn, is formed round or in the forming tool. When the sheet completelyfits to the forming tool, the pressure in the pressure dell is releasedand the diaphragm is removed, after which the formed component can betaken out of the press.

[0004] Another field in which presses of pressure cell type are used iswood compaction when a workpiece of wood is exposed to high pressure,either in a forming tool or on its own. Reasons for compacting wood are,for example, that it is desirable to increase the hardness of the wood,decrease the moisture content or to obtain a phase in pressureimpregnation.

[0005] A press of pressure cell type according to that mentioned aboveis known through SE 452 436. Said patent specification discloses a pressplant having a forged, cylindrical press body which requires large,heavy filling blocks to provide a press chamber of an essentiallyrectangular cross-section. In order to handle the large forces to whichthe press body is exposed in connection with pressing, the body is woundwith steel wire. A press of this type has to be ordered before beingmanufactured and the complicated work of forging and winding the pressbody requires several months. It usually takes 15-18 months from orderto delivery. The delivery itself is very complicated since, on the onehand, the size of a large press makes road or railway transportdifficult and, on the other, the weight amounts to tens of tonnes.

[0006] Attempts have been made to manufacture lighter presses havingless material in relation to the size than conventional presses have.However, technical problems relating to both manufacturing technique andstrength have resulted in these presses only managing a limited workingpressure that has been too low with respect to the high pressure whichis required in a modern press plant, typically up to 1200 bar.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is to provide a press ofpressure cell type which in comparison with prior-art technique ischeaper and faster to manufacture, as well as easier to handle andtransport.

[0008] Another object of the invention is to provide a method formanufacturing a press of pressure cell type, which method is quick andeasy.

[0009] These and other objects which will be evident from the followingdescription are achieved by a press of pressure cell type and a method,which have the features indicated in the appended claims.

[0010] According to one aspect of the invention, a press of pressurecell type is provided, which comprises a press chamber which is enclosedby a force-absorbing press body. The press body comprises a number ofplate-shaped lamellar means with the planes of the plates orientedparallel to the planes of the plates of adjacent lamellar means. Eachlamellar means has a through hole which has the same centre axis as thehole, said centre axis coinciding with the direction of the main axis ofthe press chamber being enclosed by the holes. Each lamellar means hasan internal edge surface which defines the hole and an external edgesurface, prestressing means which induce a compressing prestressingacting in the planes of the plates being arranged on the external edgesurface of the main part of the lamellar means. Each prestressing meanscomprises a prestressing element which is wound round a respectivelamellar means and is band-shaped and has essentially the same width asthe thickness of a lamellar means.

[0011] According to another aspect of the invention, a method isprovided for manufacturing a force-absorbing press body part. The methodcomprises the steps of

[0012] forming plate-shaped lamellar means and providing each of themwith a through hole,

[0013] inducing a lasting compressing prestress which acts in the planesof the plates in at least the majority of the lamellar means by windinga band-shaped prestressing element, which has essentially the same widthas the thickness of a lamellar means, round the external edge surface ofthe lamellar means with the purpose of causing said prestress, and

[0014] arranging each formed lamellar means having the plane of theplate oriented parallel to the plane of the plate of an adjacentlamellar means so that the through holes obtains a common centre axisand so that the lamellar means constitute a force-absorbing presschamber-enclosing press body part.

[0015] In the present application, terms describing position anddirection, such as “vertical” and “horizontal”, are used. In thisapplication, these terms are defined with respect to the arrangement ofthe press-body-forming lamellar means. Thus, each lamellar means extendsessentially vertically, whereas the direction of the main axis of thepress chamber enclosed by the lamellar means is horizontal. In theapplication, it should also be understood that “over/upwards/above” and“under/downwards/below” are defined with respect to the essentialdirection of the pressing, i.e. so that a press plate is located above adiaphragm which, in its turn, is located above a bottom plate, whichmeans that vertically is defined as perpendicular to the press plate andhorizontally as parallel to the press plate. The above-mentioneddefinitions have been indicated for sake of clarity since the press ofpressure cell type can be inclined in different manners, and due to thisfact the relative directions can vary.

[0016] The present invention is thus based on the understanding thatconsiderable improvements regarding handling and time expenditure can beprovided by means of a press body which is divided into vertical platesand has essentially maintained force-absorbing capability due to appliedprestressing means.

[0017] Consequently, the invention allows deviation from the traditionalmanufacturing process of forming an essentially homogeneous press bodyof two cylinder halves. On the contrary, it is possible to provide apress body which is inhomogeneous by the plate-shaped lamellar meansbeing arranged at a distance from one another. It has been found that anexcellent force-absorbing capability is obtained also by means of such ahollow construction which has several operational advantages that willbe described below.

[0018] A prestressing means which is arranged on the external edgesurface of a lamellar means preferably comprises a prestressing elementthat is wound round the lamellar means, such as metal wire or metalband. According to one advantageous embodiment, the prestressing elementis band-shaped and has essentially the same width as the thickness ofthe lamellar means.

[0019] If the main part of the lamellar means is prestressed by a band,the width of which (about 80-200 mm, typically 100-200 mm) essentiallyequals the thickness of the lamellar means, being wound round theexternal edge surface of these lamellar means, several advantages willbe obtained. For example, there is no essential stress concentration,but a mainly even stress distribution is obtained in the lamellar means.The shape of the lamellar means can be selected in such a manner thatoptimal stress distribution is achieved, also with relatively few turnsof the band. A suitable band is made of spring steel having a thicknessof some tens of a millimetre, typically about 0.2 mm. Due to thewinding, the lamellar means obtain a considerable length of service,which means that inspections of the press can be performed at reasonableintervals.

[0020] Conveniently, each lamellar means is provided with a number ofapertures, such as two apertures symmetrically arranged on each side ofthe hole. In an assembled position, the lamellar means are arranged insuch a manner that the apertures in the respective lamellar means havethe same centre axis as the corresponding apertures in the otherlamellar means. Preferably, a type of coupling means, such as a steelrod, for coupling lamellar means is adapted to run through a respectiveone of said series of apertures. Thus, these coupling means have alongitudinal extension which is parallel to the direction of the mainaxis of the press chamber.

[0021] The relative distance between two lamellar means is adjustablewith the aid of distance means which are arranged on the coupling means.The thickness of the distance means essentially corresponds to thedesired relative distance between two neighbouring lamellar means. Thedistance can be adapted to the stress to which the press body will besubjected when in operation. Preferably, the distance betweenneighbouring lamellar means, does not vary in the press body, but issimilar as regards all lamellar means that are adjacent to one another.The distance means are made of a relatively rigid material and theirinner diameter is larger than that of the coupling means at the sametime as their outer dimensions are considerably larger than theapertures formed in the lamellar means. It has been found to beespecially advantageous to make the thickness of the distance meansessentially the same as the thickness of the lamellar means, which meansthat they can be made of a similar sheet-metal blank.

[0022] The coupling means are tightened with the aid of suitable meansto a predetermined prestressing condition so as to avoid play and motionin the construction. At the same time the coupling means promotes thestructural stability of the construction regarding flexural rigidity,torsional rigidity and resistance to extension in all dimensions.

[0023] Between the lamellar means of the press body and the presschamber which is enclosed in the lamellar means, stress distributingelements can be arranged and extend over the press chamber.Conveniently, the stress-distributing elements cooperate with theinternal edge surface of each lamellar means and distribute stress orthrust, which arise in connection with pressing in the press chamberalong the series of lamellar means. The stress-distributing elements canconstitute parts of the wall of the press chamber.

[0024] The shape of a preferably central hole which is formed in thelamellar means is made with respect to stress concentration that canarise in critical areas and that should be avoided. Thestress-distributing elements are essentially quadrangular incross-section and cooperate with plane contact surfaces of the lamellarmeans. The plane contact surfaces define the hole in an essentiallyquadrangular configuration, the end of a predetermined contact surfaceconnecting to a contact surface which is perpendicular to saidpredetermined contact surface by means of a concave bending in the wallof the lamellar means. The radius of the concave bending is maderelatively large with the purpose of minimising stress concentrationwhich arises in the areas of the corners of the hole.

[0025] As regards the shape, an advantageous design of the internal holecan also be described as two ovals which are parallel to one another asregards their long sides and which are separated by a quadrangularspace.

[0026] Preferably, also the shape of the lamellar means is consideredwith respect to the operating conditions. Therefore, each lamellar meansis suitably given such a shape that its extension in differentdirections is essentially proportional to the expected thrust in thecorresponding directions. For example, the extension of the lamellarmeans in the vertical direction can be larger than in the horizontaldirection, if the expected thrust is larger in the vertical direction.This may be the case if the direction of the pressing is essentiallyvertical. The number of winding turns which is arranged on the lamellarmeans is suitably adapted to the shape of the lamellar means in such amanner that sufficient prestress is obtained.

[0027] As mentioned above, the invention also relates to a method formanufacturing a press body part. There are a large number of advantagesof the manufacturing technique according to the present invention, whichwill be evident in the following.

[0028] The lamellar means can be given the desired shape by milling orcutting. Different types of cutting are possible, a few examples beingwater cutting, plasma cutting and flame cutting. Those skilled in theart will realise that this is a considerably simpler process than theforming of the traditional compact press body by forging. Preferably,the lamellar means are made of hot-rolled steel sheet which subsequentlyis easily given the desired shape. In the present invention, it hasturned out to be suitable to use a sheet thickness of 80-200 mm,preferably 100-150 mm, especially 100-120 mm.

[0029] Due to the fact that the lamellar means are separate units which,by degrees, together are to form a press body, manufacture can beaccelerated considerably. Thus, various lamellar means blanks can bemachined in the respective stations at the same time. A first lamellarmeans blank can be machined in a certain station and when this lamellarmeans blank has been moved on to a subsequent station for furthermachining, a second lamellar means blank can be machined at the sametime in said certain station. This parallel managing of differentmanufacturing steps thus turns out to be very beneficial. It is alsodistinctly easier to move a relatively thin lamellar means in comparisonwith a large traditional press body. Preferably, some stations canprocess several lamellar means blanks simultaneously.

[0030] The lamellar means are easily transported to the location wherethe press of pressure cell type is intended to be used and assembled insitu.

[0031] Conveniently, a lamellar means is made in one piece.Alternatively, it can be made in several pieces and be suitablyassembled to a lamellar means. Such an assembled lamellar means isfirmly held together by means of bands which are wound round theexternal edge surface of the assembled lamellar means and/or with theaid of other locking means.

[0032] Due to the ease with which the lamellar means can be handled,unlike prior-art technique it is possible to move the press of pressurecell type relatively easily from one location to another by simpledisassembling and reassembling of the lamellar means. If a separatelamellar means is to be removed or replaced due to maintenance, this caneasily be made in the following way. The parts of the press of pressurecell type which are enclosed by the press body are suitably removedfirst from the press body, after which the lamellar means which is to beremoved is released. The actual releasing can be carried out bydisplacing a first set of coupling means, which runs through theapertures formed in the lamellar means, along the direction of the mainaxis of the press out of a first end of the press, i.e. a lamellar meanswhich defines one end of the press body. Almost at the same time, asecond set of coupling means is inserted along the direction of the mainaxis into a second end of the press body, i.e. a lamellar means whichdefines the other end of the press body. The displacement of the firstset and the insertion of the second set of coupling means are carriedout in such a manner that the lamellar means which is to be released iscontactless between said first and second set. Subsequently, thelamellar means is removed from the press.

[0033] If it is desirable to replace a removed lamellar means with a newlamellar means at the corresponding location, essentially the oppositeis carried out compared to the method described above. First of all, afirst set of coupling means is thus arranged through the apertures inthe lamellar means which are positioned on one side of the locationwhere the new lamellar means is to be incorporated, and then a secondset of coupling means is arranged through the apertures in the lamellarmeans which are positioned on the other side of said location.Consequently, the coupling means should not protrude towards the centremore than to provide space for placing the new lamellar means. When thenew lamellar means has been positioned in the press, the first set ofcoupling means is displaced through this lamellar means and the otherlamellar means into which the second set of coupling means is inserted,at the same time as this second set is taken out of the press. Finally,only the first set of coupling means will thus run through all thelamellar means which constitute the press body.

[0034] Alternatively, a lamellar means can be released and replaced bypushing out a number of the coupling means, for example half thequantity, in one direction until they are detached from the lamellarmeans at issue, and pushing out the remaining coupling means in theopposite direction until they are detached from the lamellar means atissue. Thus, some coupling means will still be positioned in a group oflamellar means, whereas the remaining coupling means will be positionedin another group of lamellar means, no supplementary coupling meansbeing required for the releasing process. When the replacement has beencarried out, the coupling means are simply pushed back to their initialposition.

[0035] When releasing and replacing a lamellar means, it is alsoconceivable to use an external stabilising beam which supports the otherlamellar means with the purpose of increasing the stability in theconstruction.

[0036] A great advantage of the present invention is the accessibilityto the internal portion of the press body. Since the lamellar meanspreferably are arranged at a distance from one another, it is possibleto easily inspect the internal edge surface of a lamellar means,defining the internal hole. An inspection or testing device is simplyinserted by the side of the lamellar means in question. If the lamellarmeans has adjacent lamellar means on both sides, it is thus possible toinsert the testing device between the lamellar means in question and oneof the adjacent lamellar means. This type of inspecting method ispossible both when the press is pressurised and in a rest position.

[0037] According to a very advantageous embodiment of the invention, aspecial internal structure is formed in the press chamber. Thisstructure comprises concentric, annular internal lamellar means whichabut against one another and which each have a hole. The internallamellar means are located in planes which are parallel to the directionof the main axis of the press chamber. Above the uppermost lamellarmeans, a press plate is arranged and below the lowermost hole, a bottomplate is arranged. Thus, the holes jointly form a space which is definedby the internal wall of the internal lamellar means, the press plate andthe bottom plate.

[0038] Preferably, the internal lamellar means have several purposes; onthe one hand, they may constitute a direct or indirect support for atool on which, for example a metal sheet is to be shaped and, on theother, they can support or fasten various parts which are active in thepress. For instance, a diaphragm which together with the press plateforms a pressure cell can be clamped between two lamellar means or theuppermost lamellar means and the press plate. Alternatively, thediaphragm can rest loosely against a shelf which protrudes from theuppermost lamellar means. A mat which is used to protect the diaphragmand is placed below the same can be fastened between two lamellar means.In a corresponding manner, the sheet can be fastened with the aid ofsuitable means.

[0039] Preferably, the internal lamellar means are integrated withlimiting means for essentially permanently limiting the expansion ofthese lamellar means. Said limiting means conveniently comprise bandswhich are wound round the external edge surface of the lamellar means ina way corresponding to that of the lamellar means which form the pressbody. Thus, no external force-absorbing device is required on the shortsides of the press chamber. The press construction can therefore be maderelatively open by the short sides of the press chamber wall, i.e. theexternal sides of the internal lamellar means, being accessible to allowinsertion and removal of the internal lamellar means. In the assembledpress, preferably some of the internal lamellar means will at the endsof the press protrude from the actual press body.

[0040] Advantageously, the internal lamellar means are loosely arrangedon the bottom plate and on one another. However, a sort of controlelement is arranged in order to ensure correct positioning. Due to thefact that the internal structure comprises lamellar means which areloosely arranged on one another, it is possible to remove them easilyone by one or several of them at the same time.

[0041] Particularly great advantages are obtained by means of theabove-described embodiment having internal lamellar means which arearranged on one another, especially as regards manufacturing, handling,freight and transport. In addition, these internal lamellar means arepreferably made of the same kind of sheet-metal blank as the lamellarmeans which form the press body. Thus, each internal lamellar means, aswell as the press-body-forming lamellar means, can be made in one pieceor in several pieces.

[0042] Also other parts included in the press are suitable to bemanufactured from a similar sheet-metal blank, for example press plate,bottom plate, distance means and stress-distributing element. This meansthat the manufacture of the parts included in the press essentially canbe made at one location and the parts are, for example, deliveredunassembled to the location where the press is to be used, after whichthe press is assembled in situ. Preferably, the press of pressure celltype is assembled in situ on a suitable type of foundation which keepsthe construction in position.

BRIEF SUMMARY OF THE DRAWINGS

[0043]FIG. 1 is a side view of a lamellar means which is included in apress of pressure cell type shown according to one embodiment of theinvention.

[0044]FIG. 2 is a perspective view in cross-section of the lamellarmeans in FIG. 1.

[0045]FIG. 2B illustrates one example of a device for locking a band.

[0046]FIG. 3 is a top view of a press of pressure cell type according toone embodiment of the invention.

[0047]FIG. 4 is an end view of the press of pressure cell type in FIG.3.

[0048]FIG. 5 is a side view, partly in cross-section, of a press ofpressure cell type according to one embodiment of the present invention.

[0049]FIG. 6A shows the press of pressure cell type in cross-sectionalong the line B-B in FIG. 5.

[0050]FIG. 6B is a top view of a detail in FIG. 6A.

[0051] FIGS. 7A-7E schematically illustrate different variants oflamellar means.

DETAILED DESCRIPTION OF THE DRAWINGS

[0052]FIG. 1 is a side view of one embodiment of a lamellar means 10which is included in a press of pressure cell type according to theinvention. FIG. 2 is a perspective view in cross-section of the lamellarmeans 10 in FIG. 1. The cross-section is made along the line A-A inFIG. 1. These figures show that the lamellar means 10 is plate-shapedand thus has two side surfaces or main surfaces 12. The circumference ofthe lamellar means 10 is defined by a relatively narrow,circumferential, external edge surface 14. The lamellar means 10 isprovided with a central through hole 16 which is defined by an internaledge surface 18. The hole 16 is essentially quadrangular, but withoutactual corners. The “corner regions” are instead rounded and bendinwards into the wall so that a larger hole area is obtained. The radiiof these inward bends are made relatively large with the aim ofminimising the stress concentration that arises in the corner regions.

[0053] The lamellar means 10 is essentially quadrangular and has roundedcorners. The shape of the lamellar means is adapted to the expectedthrust which arises in connection with the pressing. Thus, the materialquantity or the distance between the internal and the external edgesurface is larger vertically than horizontally since the main directionof pressing is vertical.

[0054] A plurality of turns of a band 20 of spring steel are wound roundthe external edge surface 14 of the lamellar means 10, the band 20having a width which essentially corresponds to the thickness (about 120mm) of the lamellar means 10. The height of the layer of band is about100 mm and the layer can consist of one single long band or severaljoined bands. When the lamellar means 10 is being manufactured, the band20 is wound round the same during resistance so that a compressiveprestress is permanently induced in the lamellar means 10. As shown inFIG. 2 (not in FIG. 1), the lamellar means 10 can be provided with atype of control element 22 adjacent to the external edge surface 14 ofthe lamellar means 10 with a view to facilitating the winding of theband. This control element 22, which is shown more clearly in FIG. 2B,also operates as a device for locking the winding of the band. Thedevice 22 comprises two side pieces 24 which are intended to be fastenedon one side each of the lamellar means 10. A transverse roller 26 isfastened between the side pieces and is suitably intended to be arrangedin a small hollow (not shown) in the external edge portion 14 of thelamellar means 10. The roller 26 is provided with a slit 28 into whichthe band 20 is inserted. When the locking is ready, the band is woundround the lamellar means 10. By the end of the winding process, i.e. inthe outermost layer, there is essentially no tension. However, it ispossible to lock also this end of the band using the technique known tothose skilled in the art.

[0055] Apart from the central hole 16, the lamellar means 10 is formedwith four circular apertures 30, two above and two below the hole. Theapertures 30 are intended to receive the coupling means which will bepresented in more detail in the following.

[0056] The lamellar means 10 is formed by hot-rolled steel plate havinga thickness of 120 mm, preferably by milling or cutting. It is possibleto assemble the lamellar means 10 from two or more parts, whichsubsequently by means of the turns of the band are connected to anintegral unit. The height and width of the lamellar means are typicallyabout 4000 mm and 3500 mm, respectively.

[0057]FIG. 3 is a top plan view of a press 40 of pressure cell typeaccording to one embodiment of the invention. A number of lamellar means42 are arranged next to one another in such a manner that the plane ofthe plate or main surface of each lamellar means 42 is parallel to theplate plane of the other lamellar means 42. The lamellar means 42 areequidistantly spaced from one another and they are of essentially thesame size and thickness. The central holes are identical in all thelamellar means 42. The lamellar means 42 are positioned in such a mannerthat the central holes have a common centre axis, along which the serialholes or the internal edge surfaces of the lamellar means together inthe form of a lattice define a space for housing a press chamber 44. Thedirection of the main axis X of the press chamber 44 coincides with thecentre axis of the central holes. FIG. 3 shows an upper press chamberwall 46 and two side walls 48 which are perpendicular thereto.

[0058]FIG. 4 is an end view of the press 40 of pressure cell type inFIG. 3. From the side it is thus possible to see the main surface of anend lamellar means 42′ having the central hole 52. This lamellar means42′ contains in the hole 52 together with the holes of the otherlamellar means 42 a press chamber in which, for example, a workpiece ofsheet-metal or wood is intended to be machined. In the upper portion ofthe holes, a press plate 54 is arranged in contact with the internaledge surface of the lamellar means 42. Thus, the press plate 54 canconstitute the upper press chamber wall 46 shown in FIG. 3. Furthermore,FIG. 4 shows that a bottom plate 56 is arranged in contact with theinternal edge surface of the lamellar means 42 in the lower portion ofthe holes. Between these plates 54, 56, a number of plate-shapedinternal lamellar means 58 which abut against one another are arranged.The main surfaces or the plate planes of these internal lamellar means58 have an extension which is parallel to the direction of main axis ofthe press chamber. FIG. 4 also shows that the longitudinal side walls 48of the press chamber shown in FIG. 3 have a height which essentiallycorresponds to the distance between the upper press plate 54 and thebottom plate 56. The internal lamellar means 58 are during pressingexposed to an internal overpressure, and because of this fact thelamellar means aim at expanding, whereby high tensile stress in theinternal periphery of the internal lamellar means 58 is generated. Forthis reason, a generator 60 of horizontal force is arranged adjacent tothe left side wall in the figure. This generator 60 predeforms andprestresses the deformation zones in the internal lamellar means.

[0059]FIG. 5 is a side view, partly in cross-section, of a press 70 ofpressure cell type according to one embodiment of the present invention.A central portion of the press 70 of pressure cell type is cut out ofthe Figure, to the left of the central portion an ordinary side view ofthe press being shown and to the right of the central portion a sideview in cross-section of the press being shown. Thus, to the left in theFigure the external edge surface 74 of the lamellar means 72 which arecomprised in the press is shown. An upper press plate 76 and a bottomplate 78 run through the central holes of the lamellar means 72. Betweenthese plates, two internal lamellar means 80 a, 80 b which abut againstone another are arranged. Through circular apertures which weredescribed in connection with FIG. 1 and FIG. 2, in all lamellar meansincluded in the press body, run coupling means 82 (two of which areshown), for example a steel rod having threaded ends. The lamellar means72 are kept at a distance from one another by the fact that round eachcoupling means 82, between the lamellar means 72, there are distancemeans 84 having a thickness that is as large as the desired distancebetween the lamellar means. The distance means 84 are made of arelatively rigid material and their inner diameter is larger than thatof the coupling means 82 at the same time as their external measures areessentially larger than the apertures arranged in the lamellar means 72.At the two external ends of the coupling means 82, outside therespective external lamellar means which are included in the press body,there are stop devices 86 of which at least one has a fixing andclamping mechanism which is complementary to the coupling means. In thecase when the coupling means 82 comprises a rod being threaded at itsends, the attaching and stressing mechanism can comprise a washer and anut, the washer having external measures which are essentially largerthan the coupling apertures of the external lamellar means. The fourcoupling means 82 are thus tightened to a predetermined prestresscondition. This eliminates play and motion in the construction and atthe same time contributes to the structural stability of theconstriction as regards flexural rigidity, torsional rigidity andresistance to extension in all dimensions.

[0060] As already mentioned, the right part of FIG. 5 is a side view incross-section of the press 70 of pressure cell type. The cross-sectionis made at the centre of the press, i.e. along the main axis of thepress chamber. FIG. 5 shows that the lamellar means 72 which constitutethe press body are wound with a band 88 on the respective external edgesurfaces. Moreover, the Figure shows that also the internal horizontallamellar means which abut against one another are wound with a band.This winding 88 of the internal lamellar means 80 a, 80 b with a band isintended to essentially permanently limit expansion of the internallamellar means, i.e. they must be able to withstand the forces which areformed in the press chamber. The internal lamellar means 80 a, 80 b areannular, which thus means that they define an internal, open space whichis comprised in the press chamber. In addition, FIG. 5 shows an upperinternal lamellar means 80 a and a subjacent lower internal lamellarmeans 80 b. A diaphragm 90 is arranged in the open space of the upperinternal lamellar means 80 a. The diaphragm 90 has a seal 92 against thepress plate 76 and forms a pressure cell therewith. During operation, apressure medium is supplied to the pressure cell in such a manner thatthe diaphragm 90 expands. The open space 94 of the lower internallamellar means 80 b is intended to contain a tool. A metal sheet whichis to be pressed against the tool is suitably arranged above the tool,the diaphragm 90, when being pressurised, expanding and being formed onthe tool, which means that the metal sheet that is located therebetweenis also formed on the tool. Besides, the Figure shows that a mat 96 isarranged just below the diaphragm. The carpet 96 takes part in theforming of the plate and at the same time protects the diaphragm againstwear. Adjacent to the internal wall of the lower internal lamellar means80 b, a filling element 98 of rubber is arranged with the aim ofdistributing forces and of supporting the tool. If a piece of wood is tobe pressed, this can be carried out without any tools.

[0061]FIG. 6A shows a press of pressure cell type in cross-section alongthe line B-B in FIG. 5. This Figure shows a hydraulic compensator orgenerator 100 of horizontal force, which thus affects the internallamellar means horizontally. Unlike the integrated wound bands 88, thisgenerator is separate from the internal lamellar means 80 a, 80 b and isadapted to apply these radially prestressing or predeforming forces (cf.FIG. 4). Conveniently, the generator comprises hydraulic pistons. Asshown in FIGS. 5 and 6a, the upper internal lamellar means 80 a has suchan extension that its upper portion encloses the press plate 76, theinternal dimension of the lamellar means 80 a essentially correspondingto the outer dimension of the press plate 76. This contributes tosatisfactory sealing of the pressure cell.

[0062]FIG. 6B is a partial top view of the lower internal lamellar means80 b in FIG. 6A. Thus, it is shown that this lamellar means 80 b has theform of a “running track”, i.e. its wall is defined by two parallelstraight portions which at the ends are connected to one another byconvex semicircles. In the space just inside the respective semicircles,a semi-circular filling block or end block 102 of resilient material,such as rubber, is fitted so that the remaining free space isquadrangular. The purpose of the end blocks 102 is, among other things,to serve as support for the tool. Straight resilient supports 104 whichare parallel to the direction of the main axis of the press chamber canalso be arranged adjacent to the straight wall portions. These supports104 and end blocks 102 (which correspond to the filling element 98 inFIG. 5) also have a protecting function in the sense of protecting andprolonging the service length of the internal lamellar means bydistributing forces which are generated during pressing operations.Since the internal lamellar means 80 a, 80 b are prestressed by theturns of the band 88, no external limiting means are required andtherefore, for example, the semi-circular portions can protrude from theends of the press body as shown in FIG. 3 and FIG. 5. Since the internallamellar means 80 a, 80 b protrude, they are relatively easilyaccessible, which is time-saving when metal sheets are removed, toolsare replaced, diaphragms are replaced etc.

[0063] FIGS. 7A-7E schematically illustrate different variants oflamellar means. As these Figures show, lamellar means can be made indifferent sizes and have different shapes. The lamellar means shown inFIG. 7A essentially has the shape of a square having rounded edges andis suitably used for a press body which gives a load space of100×200×2500 mm³. The working pressure in such a space is typically 1200bar. FIG. 7B illustrates another possible shape which together withidentical lamellar means forms a press body which gives a load spacehaving the dimensions 125×500×1500 mm³ and a typical working pressure of700 bar. FIG. 7C illustrates a lamellar means which is composed ofseveral parts and thus, unlike the previously shown lamellar means, isnot made in one piece. In this case, two central parts 120, 122 togetherform the central hole. Two external parts 124, 126 are arranged at theexternal edge of the respective central parts in such a manner that alamellar means of a suitable shape is provided. The four parts includedin the lamellar means are held together by the turns of the band (notshown). This lamellar means is somewhat smaller than, but hasessentially the same shape as, the lamellar means in FIG. 7E, which,however, is made in one piece and provides a load space having thedimensions 200×1100×200 mm³. FIG. 7D shows another variant of a lamellarmeans which is made of several parts. In this case, there are fouressentially uniform parts which together form a lamellar means.Consequently, an upper left part 130, a lower left part 132, an upperright part 134 and a lower right part 136 are shown. These are heldtogether by means of the previously described turns of the band (notshown). As a possible alternative, a lamellar means corresponding tothat shown in FIG. 7D could be made of two halves only, such as a lefthalf and a right half, instead of four parts. The lamellar means in FIG.7D provides with other corresponding lamellar means a load space havingthe dimensions 400×1600×4000 mm³.

[0064] Those skilled in the art will thus understand from the examplesillustrated above that the lamellar means can be made in one or morepieces, be given different shapes and be made in different sizes asregards both external and internal dimensions.

[0065] Although some preferred embodiments have been described above,the invention is not limited thereto. It is thus possible to usevariants of the internal structure other than those described. Thedesign of the individual lamellar means can also be varied in accordancewith the current needs. It should thus be understood that a plurality ofmodifications and variations can be provided without deviating from thescope of the present invention which is defined in the appended claims.

1. A press (40, 70) of pressure cell type, which press comprises a presschamber being enclosed by a force-absorbing press body which comprises anumber of plate-shaped lamellar means (10, 42, 42′, 72) with the planesof the plates oriented parallel to the planes of the plates of adjacentlamellar means, each lamellar means having a through hole (16, 52) whichhas the same centre axis as the hole of the adjacent lamellar means,said centre axis coinciding with the direction of main axis (X) of thepress chamber being enclosed by the holes and each lamellar means havingan internal edge surface (18) which defines the hole and an externaledge surface (14, 74), characterised in that prestressing means (20, 22,24, 26, 28, 88) which induce a compressing prestress acting in theplanes of the plates are arranged on the external edge surface of themain part of the lamellar means, each prestressing means comprising aprestressing element (20, 88) which is wound round a respective lamellarmeans, is band-shaped and has essentially the same width as thethickness of a lamellar means.
 2. A press of pressure cell type asclaimed in claim 1, wherein the lamellar means are arranged at adistance from one another, preferably at a distance that corresponds tothe thickness of the lamellar means.
 3. A press of pressure cell type asclaimed in claim 1 or 2, wherein each lamellar means is provided with anumber of apertures (30) which are aligned with the correspondingapertures of the other lamellar means so that a number of series ofapertures are formed, which are parallel to the direction of the mainaxis of the press chamber, a coupling means (82) for coupling lamellarmeans being adapted to run through a respective one of said series ofapertures.
 4. A press of pressure cell type as claimed in claim 3,wherein distance means (84) are arranged on said coupling means forcontrolling the relative distance of the lamellar means.
 5. A press ofpressure cell type as claimed in any one of claims 1-4, whereinstress-distributing elements (46, 48, 54, 56, 76, 78) extending over thepress chamber are arranged between the lamellar means of the press bodyand the press chamber which is enclosed by said lamellar means, thestress-distributing elements cooperating with the internal edge surfaceof the lamellar means.
 6. A press of pressure cell type as claimed inclaim 5, wherein the stress-distributing elements constitute parts ofthe wall (46, 48) of the press chamber.
 7. A press of pressure cell typeas claimed in claim 5 or 6, wherein the stress-distributing elementsdefine a portion in the press chamber which in cross-section has anessentially straight quadrangular configuration, and cooperate withplane contact surfaces of the lamellar means.
 8. A press of pressurecell type as claimed in claim 7, wherein the plane contact surfaces ofthe lamellar means define the hole in essentially a quadrangularconfiguration, the end of a predetermined contact surface connecting toa contact surface being perpendicular to said predetermined contactsurface by means of a concave bending in the wall of the lamellar means.9. A press of pressure cell type as claimed in any one of claims 1-8,wherein each lamellar means has been given such a shape that itsextension in different directions is essentially proportional to theexpected thrust in the corresponding directions.
 10. A press of pressurecell type as claimed in claim 9, wherein the material quantity or thedistance of each lamellar means between the internal and the externaledge surface is larger in the direction of pressing than in thedirection perpendicular thereto.
 11. A press of pressure cell type asclaimed in any one of claims 1-10, wherein an internal structure isarranged in the press chamber, which structure is made up of concentriclamellar means (58, 80 a, 80 b) abutting against one another and havingthrough holes (94) and being located in planes which are parallel to thedirection of the main axis of the press chamber, a workpiece beingintended to be machined in the space (94) which is formed of the holesof the concentric lamellar means.
 12. A press of pressure cell type asclaimed in claim 11, wherein the lamellar means in the internalstructure round the external edge surfaces are wound with a band (88) ofessentially the same width as the thickness of the lamellar means forprestressing thereof.
 13. A press of pressure cell type as claimed inclaim 11 or 12, wherein the lamellar means in both the internalstructure and in the press body are made of the same material and havethe same thickness.
 14. A press of pressure cell type as claimed in anyone of claims 1-13, wherein at least one, preferably each, lamellarmeans is made in one piece.
 15. A press of pressure cell type as claimedin claims 1-14, wherein at least one lamellar means is made in severalpieces (120, 122, 124, 126, 130, 132, 134, 136).
 16. A press of pressurecell type as claimed in any one of claims 1-15, wherein the lamellarmeans are made of sheet steel.
 17. A method for manufacturing aforce-absorbing press body part intended to enclose a press chamber,characterised by the steps of forming plate-shaped lamellar means (10,42, 42′, 72) and providing each of them with a through hole (16, 52),inducing a lasting compressing prestress which acts in the planes of theplates in at least the majority of the lamellar means by winding aband-shaped prestressing element (20, 88), which has essentially thesame width as the thickness of a lamellar means, round the external edgesurface of the lamellar means with the purpose of causing saidprestress, and arranging each formed lamellar means having the plane ofthe plate oriented parallel to the plane of the plate of an adjacentlamellar means so that the through holes obtain a common centre axis andso that the lamellar means constitute a force-absorbing,press-chamber-enclosing press body part.
 18. A method as claimed inclaim 17, wherein the lamellar means are arranged at a distance from oneanother, preferably at a distance that corresponds to the thickness ofthe lamellar means.
 19. A method as claimed in claim 17 or 18, whichcomprises the step of giving the lamellar means the desired shape bymilling.
 20. A method as claimed in claim 17 or 18, which comprises thestep of giving the lamellar means the desired shape by cutting, such aswater cutting, plasma cutting, flame cutting etc.
 21. A method asclaimed in any one of claims 17-20, which comprises the step of makingthe lamellar means of hot-rolled sheet steel.
 22. A method as claimed inany one of claims 17-21, which comprises the step of making the lamellarmeans of sheet steel having a thickness of 80-200 mm, preferably 100-150mm, in particular 100-120 mm.
 23. A method as claimed in any one ofclaims 17-22, which comprises making the lamellar means in sequence in anumber of stations according to the steps of machining a first lamellarmeans blank in an appropriate station, conveying said first lamellarmeans blank to a subsequent station for further machining, and machininga second lamellar means blank in said appropriate station at the sametime as said first lamellar means blank is being machined in saidsubsequent station.
 24. A method as claimed in claim 23, in which one ofsaid stations comprises parallel machining of a plurality of lamellarmeans blanks.
 25. A method as claimed in any one of claims 17-24, whichcomprises the step pf assembling the lamellar means to a press body atthe location where a press (40, 70) of pressure cell type is to be used,the coupling means (82) being arranged in the lamellar means in such amanner that they are held together as a unit.
 26. A method as claimed inany one of claims 17-25, which comprises the step of making the lamellarmeans in one piece.
 27. A method as claimed in claims 17-26, whichcomprises the step of making the lamellar means in several pieces (120,122, 124, 126, 130, 132, 134, 136).
 28. A lamellar means (10, 42, 42′,72) of a press body part, which is plate-shaped and has a through hole(16, 52), the lamellar means having an internal edge surface (18) whichdefines the hole, characterised in that the lamellar means has anexternal edge surface (14, 74) on which a prestressing means (20, 22,24, 26, 28, 88) is arranged, which induces a compressing prestressacting in the plane of the plates of the lamellar means, theprestressing means comprising a prestressing element (20, 88) which iswound round the lamellar means and is band-shaped and has essentiallythe same width as the thickness of a lamellar means.
 29. A lamellarmeans as claimed in claim 28, wherein the lamellar means is made ofsheet steel.